A supermajority or a qualified majority is a requirement for a proposal to gain a specified greater level of support than a 50% simple majority. In some jurisdictions, for example, parliamentary procedure requires that any action that may alter the rights of a minority has a supermajority requirement (such as a two-thirds majority). Changes to constitutions, especially those with entrenched clauses, commonly require supermajority support in a legislature. A supermajority is absolute if the required percentage or fraction is based on the entire membership rather than on those present and voting.

A majority is a potentially ambiguous supermajoritarian requirement. There are two kinds of supermajority: the simple (based on those present) or the absolute (based on those qualified to vote). Clarity is required over voter qualification and also what is done about abstentions.

An unqualified or simple two-thirds vote requires that the number of votes in favor must be at least twice the number of votes against. Abstaining votes or neutral votes are not considered in a simple two-thirds vote.

An absolute two-thirds vote requires that at least two-thirds of the entire membership of a body vote in favor. (The Constitution of India requires, in numerous cases, a motion supported both by two-thirds of MPs voting and by an absolute majority of all MPs).

In parliamentary procedure where a two-thirds vote is required, rather than speaking of a two-thirds majority the unambiguous phrases such as "two-thirds of those present and voting", "two-thirds of those present" (which has the effect of counting abstentions as votes against the proposal), or "two-thirds of the entire membership" ("two-thirds of those members duly elected and sworn" in American politics) are used.

The US Mason's Manual notes, "A deliberative body cannot by its own act or rule require a two-thirds vote to take any action where the constitution or controlling authority requires only a majority vote. To require a two-thirds vote, for example, to take any action would be to give to any number more than one-third of the members the power to defeat the action and amount to a delegation of the powers of the body to a minority."[1]

An absolute majority or majority of the entire membership is a voting basis that requires that more than half of all the members of a body (including those absent and those present but not voting) to vote in favour of a proposition in order for it to be passed.[2] In practical terms, it means abstention from voting is equivalent to a no vote. It may be contrasted with a simple majority which only requires a majority of those actually voting to approve a proposition for it to be enacted.

By way of illustration, in February 2007 the Italian Government fell after it won a vote in the Italian Senate by 158 votes to 136 (with 24 abstentions). The government needed an absolute majority in the 318 member house but fell two votes short of the required 160 when two of its own supporters abstained.[4]

A majority of the fixed membership is a supermajority that is based on the total number of the established fixed membership of the deliberative assembly. It is used only when a specific number of seats or memberships is established in the rules governing the organization, e.g. a board of seven members.

This majority of the fixed members is set at any number greater than one-half of the total possible memberships or seats. For example, on an 8-member board, the majority of the fixed membership is 5 or more.

Most private organizations do not use this standard. The popular parliamentary manual Robert's Rules of Order does not require it for any action. It is sometimes the standard set to adopt some or all actions in state and local government legislative bodies in the United States.

It is possible for organizations that use majority of the fixed membership to be caught in a stalemate if at least half the membership consists of vacancies, making it impossible to perform any actions until those vacancies are filled.

However, the United Nations Security Council does require a supermajority of the fixed membership on substantive matters (procedural matters require a simple majority of those present and voting). According to Article 27 of the United Nations Charter, at least nine of the Security Council's 15 members (i.e., a three-fifths supermajority) must vote in favor of a draft resolution in order to achieve passage. Specifying the fixed membership has the effect of making abstentions count as votes against—absences are not normal but would be treated the same way.

This is useful for the five permanent members of the Council (the United States, the Russian Federation, the People's Republic of China, the United Kingdom, and France) because a vote against from any one of them constitutes a veto, which cannot be overridden. Permanent members who do not support a measure, but are unwilling to be seen to block it against the wishes of the majority of the Council, tend to abstain; abstentions by veto powers are generally seen by close observers of the UN as the equivalent of not vetoing votes against and have the same impact on the decision of the Security Council.

The Article 368 of the Indian Constitution requires a super majority of two-thirds of members present and voting in each house of Indian Parliament, subject to at least by a majority of the total membership of each House of Parliament, to amend the constitution. In addition, in matters affecting the states and judiciary, at least one half of all the states need to ratify the amendment.

According to the Danish Constitution, the Danish Parliament may delegate specific parts of the country's sovereignty to international authorities, provided that five-sixths of its members approve of the bill.

In the Northern Ireland Assembly certain resolutions must receive "cross community support", or the support of a minimum number of MLAs from both main communities.

Scotland first got the opportunity to vote in a referendum on proposals for devolution in 1979, and though a majority of those voting voted 'Yes', the referendum legislation also required 40% of the electorate to vote 'Yes' for the plans to be enacted.

Amendments to the Constitution may be proposed in one of two ways: a two-thirds super majority votes of each house of Congress or a constitutional convention called by two thirds (currently 34) of the states. Once proposed, the amendment must be ratified by three quarters (currently 38) of the states.

Many state constitutions allow or require amendments to their own constitutions to be proposed by super majorities of the state legislature; these amendments must usually be approved by the voters at one or more subsequent elections. Michigan, for instance, allows the Legislature to propose an amendment to the Michigan Constitution; it must then be ratified by the voters at the next general election (unless a special election is called).[5]

Congress may pass bills by simple majority votes. If the president vetoes a bill, Congress may override the veto by a two-thirds super majority of both houses.

A treaty may be ratified by a two-thirds super majority of the Senate.

Section 4 of the 25th Amendment gives Congress a role to play in the event of a presidential disability. If the vice president and a majority of the president's cabinet declares that the president is unable to serve in that role, the vice president becomes acting president. Within 21 days of such a declaration (or, if Congress is in recess when a president is disabled, 21 days after Congress reconvenes), Congress must vote by two-thirds super majorities to continue the disability declaration; otherwise, such declaration expires after 21 days and the president resumes his or her role. While Section 3 of this amendment (in which the president declares himself or herself disabled) has been invoked three times, Section 4 has yet to be invoked.

The House may, by a simple majority vote, impeach a federal official (such as the president, vice president, or a federal judge). Removal from office requires a two-thirds super majority of the Senate. In 1842, the House failed to impeach president John Tyler. In 1868, the Senate fell one vote short of removing president Andrew Johnson following his impeachment. In 1999, efforts to remove Bill Clinton following his impeachment in 1998 fell just short of a simple majority, and 17 votes short of the two-thirds super majority. The impeachment procedure was last used in 2010, when Judge Thomas Porteous was removed from office. Each chamber may expel one of its own members by a two-thirds super majority vote; this last happened when the House expelled James Traficant in 2002.

Theoretically, a two-thirds supermajority in the Senate is 67 out of 100 senators, while a two-thirds super majority in the House is 290 out of 435 representatives. However, since few votes take place with every seat in the House filled and representative participating, it does not often require 67 senators or 290 representatives to achieve this super majority.

Apart from these constitutional requirements, a Senate rule requires a super majority of three fifths to move to a vote through a cloture motion, which closes debate on a bill or nomination, thus ending a filibuster by a minority of members. In current practice, the mere threat of a filibuster prevents passing almost any measure that has less than three-fifths agreement in the Senate, 60 of the 100 senators if every seat is filled and voting.